Real-World Analysis of 3,843 Unrelated Donors (URDs) for 455 Allograft Candidates Reveals Low URD Availability with Marked Racial/ Ethnic Disparities: Implications for Transplant Center & Registry Operations

Introduction Despite global URD registry size, the degree to which URD availability is a transplant barrier is unknown. Methods We evaluated URD availability 1/2020-12/2022 in 455 consecutive adult patient (pts) with acute leukemia, MDS or MPN who had a formal search & for whom at least one 5-8/8 URD was requested for confirmatory typing (CT). We hypothesized URD availability is a barrier for underserved racial/ ethnic pts & is not improving. Results Of 455 pts, 74% (335/455) had European (EURO) & 26% (120/455) non-European (non-EURO) ancestry. For the 455 pts, 3,843 URDs were requested for CT: 71% (2,730/3,843) for EURO [1,411/2,730 (52%) domestic] & 29% (1,113/3,843) for non-EURO [729/1,113 (65%) domestic] pts. Among 2,775 URDs with available donor readiness scores, more URDs requested for non-EURO pts had scores < 30%: 168/702 (24%) vs EURO pts: 32/2,073 (2%), p < .001. 303/455 (67%) pts were transplanted: 266 5-8/8 URD, 20 Cord Blood (CB), 17 haplo.Figs 1A-C & 2A-C show URD availability.• URD CTs/ pt: more non-EURO pts (vs EURO pts) had > 10 URDs requested (p = .045), < 5 URDs available for CT (p < .001), & ≥ 5 URDs unavailable (p < .001).• URD workups/ pt: for over one-quarter of pts (134/455, 29%), 3-5 URDs were requested. More non-EURO pts (vs EURO pts) had < 2 URDs available for workup (p = .007) & ≥ 2 URDs unavailable (p = .017).• URD availability for CT & workup: only half (2,039/3,843, 53%) were available for CT with < 70% (604/889, 68%) available for workup. URDs requested for non-EURO pts were less likely to undergo CT or workup (each p < .001). African & non-Black Hispanic pts had markedly worse URD availability. For African pts, only one-third (150/458, 33%) were available for CT with less than half (32/77, 42%) available for workup; less than half (120/258, 47%) requested for non-Black Hispanic pts underwent CT with less than two-thirds (37/61, 61%) available for workup.• URD availability over time: This did not improve for non-EURO pts post-pandemic (2022).• URD provision: Of 339 pts with ≥ 1 URD who underwent workup, 12% had no URDs available within 14 days of the 1st proposed collection date. Of 263 5-8/8 URD recipients, over one-third (39%) were not transplanted with the primary URD selected. Conclusions The significant limitations of & ongoing disparities in URD availability have major implications for transplant center & registry operations. Centers should pursue, & registries should permit, simultaneous pursuit of multiple URDs, especially for non-EURO pts (likely many for African & non-Black Hispanic pts). At the outset, the minimum acceptable HLA-match must be decided if few or no 8/8 URDs are likely & if haplo &/or CB grafts will be considered. Centers are obliged to inform pts of poor URD searches/ availability & not pursue futile searches. Finally, while registries should address high URD attrition & speed donor procurement, use of all alternative donors is needed to facilitate transplantation for all.